The invention relates to an electro-pneumatic signal converter, having a piezo-electric bending element which bends when an electrical voltage is applied and controls a pneumatic signal transmitter.
For the electrical actuation of pneumatic circuits or pneumatic appliances solenoid valves are used practically exclusively. When an electrical voltage is applied the magnet coil draws an armature against the force of a return spring, and the armature actuates a pneumatic control valve. When the voltage is switched off the return spring causes the control valve to be restored to the rest position. The said solenoid valves are relatively robust and have proved successful many times in practice. In comparison with electronic circuits, however, the solenoid valves operate relatively slowly, as a magnetic field must be produced before the switching motion is performed. In addition, they have a high energy requirement since the excited magnet coil has a continuous energy consumption and produces heat. The solenoid valves can therefore often only be integrated in modern control devices with difficulty.
The International Application 80/01826 discloses an electro-pneumatic signal converter with a tongue-shaped piezo-electric bending element which at one end is firmly clamped and at the other end controls the output of a pneumatic nozzle. As in the case of the known mechanico-pneumatic signal converters with a deflecting plate controlling the nozzle, a choke is arranged upstream of the nozzle so that the pneumatic pressure in the space between the nozzle and the choke is altered according to the deflection of the piezo-electric bending element. This known signal converter thus produces a pneumatic output signal which is proportional to the voltage applied to the piezo-electric bending element. The disadvantage of this is that the nozzle has a continuous air consumption and operation can only take place with low pressures and pressure fluctuations. The electrical and pneumatic circuit complexity required for the practical application of this device is therefore relatively substantial.
Electro-pneumatic signal converters are already known in which the pneumatic valves are controlled with the aid of piezo elements which are joined to form columns and which are prolonged or shortened in the axial direction when electrical voltages are applied. In these designs a substantial mechanical effort is necessary for transmitting the mechanical control movements, as tolerances take effect more intensively in manufacture and lead to inaccuracies in control. In addition, the function of the converter is impaired by heat expansion of the piezo-electric columns.
The object of the invention is to improve the hitherto known electro-pneumatic signal converters in such a way that they have a smaller power requirement and operate without significant energy consumption, and they should also be simple to produce and robust in operation.